Recent battery technology, such as is set forth in U.S. Pat. No. 3,476,602 discloses the use of a molten alkali metal anode/anolyte and a molten sulfur/alkali metal sulfide catholyte separated by an alkali metal ion-permeable membrane/electrolyte. A cathodic current collector, or "cathode" is immersed in the catholyte. When the anode and cathode are connected through an external electrical circuit, the electrons are discharged to the circuit from the anode with the formation of positively charged alkali metal ions. These ions migrate through the membrane into the catholyte. Negatively charged sulfide (polysulfide) ions are formed in the catholyte by interaction of sulfur at the cathode surface with electrons received from the external circuit.
In one embodiment of such a battery, the membrane is in the form of a multiplicity of sodium-filled hollow glass fibers closed at one end and open at the other. The open ends of the fibers communicate with a reservoir of molten sodium and the fibers are immersed in a molten polysulfide catholyte, with the anolyte (sodium) and catholyte being separated by a tubesheet or header which encompasses a portion of the fibers in a sealing arrangement. That is, the glass and glass-ceramic hollow fibers or other electrolyte separators are sealed in place as a bundle in a header by adhesives such as glazing or potting compounds, solder glass, and the like materials. A large anode area may be afforded by closely spacing a large number of the fine hollow fibers in a given cell or battery volume.
U.S. Pat. No. 4,112,203 discloses a battery cell having a large number of fine hollow glass fiber lengths, with their lower end closed and their upper ends open, passing through a tubesheet in sealing arrangement therewith. The open ends of the fibers communicate with a molten alkali metal in an anolyte cup and the portions of the fibers below and depending downwardly from the tubesheet are immersed in a corresponding alkali metal polysulfide melt. The fiber lengths are disposed generally parallel to one another in a continuous spiral of generally concentric vertical rows and constitute a generally cylindrical bundle.
Disposed between the rows of fibers within the bundle and wrapped around the bundle at least once is a cathodic current collector consisting of a thin, flexible, elongated sheet of metal or metal alloy, such as aluminum foil, preferably protectively coated with graphite or molybdenum disulfide. The cathode sheet may be pierced by perforations to facilitate catholyte flow into and out of the spaces between the cathode sheet and the fibers, and the sheet is suitably connected to a catholyte lead for connecting the battery cell to an external electrical circuit. In a like manner, an anode lead passes through the top of the anolyte cup and is utilized to connect the battery cell to an external electrical circuit.
The tubesheet or header of the prior art which joins the hollow fibers together and provides a seal between the sodium anode and the sodium sulfide cathode chambers, is generally formed of a frit or solder glass material which is softer than the hollow capillary fibers. When the frit or solder glass is fired, it fuses into a porous mass and seals to the outer walls of the hollow fibers without softening the fibers, however the porous nature of the resulting tubesheet promotes leakage, and the expansion difference between the tubesheet glass and the glass of the fibers promotes the breakage of such fibers. Further, the softer tubesheet glass may yield or flow excessively at battery cell operating temperatures which may be in excess of 300.degree. C. in larger sized cells. Further, in view of the aluminum foil interposed between rows of such capillary fibers, the bundle of fibers is rather fragile since each fiber is only connected at one end to the tubesheet and hangs freely downwardly therefrom.
United Kingdom patent application No. GB2017391A, published Oct. 3, 1979, entitled A Sodium/Sulphur Cell, addresses itself to the problems of suspending a plurality of hollow open ended fibers from a tubesheet, and proposes to overcome such problems by positioning a metal wire within each fiber and sealing the fibers at both ends, with the metal wire embedded within and projecting outwardly from at least one sealed end of the fiber. As pointed out by the published application, an appropriate connection can be made between the sealed fiber and a closing plate for the cell in a manner capable of withstanding great mechanical strain and with fewer breakage problems, by closing the end of the fiber to be sealed and by sealing the conductor wire in the closed end and into the closing plate. It is thus possible, according to the published application, to fusion seal one closed end of the fiber having a wire passing therethrough directly to a closing plate for the battery cell. Thus, each fiber becomes an individual closed chamber, which chambers are not in open communication with one another.
It thus has been an object of the present invention to provide an alkali metal/sulfur cell or battery in which the standard tubesheet which separates the anolyte and catholyte is eliminated as such, by fusing the outer walls of hollow fibers forming the ion-permeable electrolyte together as a solid sealing mass adjacent open ends thereof, in such a manner so as to fill the interstices between such fibers with the glass composition of the fibers while retaining the interiors of such fibers in open communication with an adjacent chamber.
A further object of the invention has been to provide an alkali metal/sulfur cell or battery wherein the hollow fibers of the bundle forming the ion-permeable membrane or electrolyte are sealed together along adjacent portions of their longitudinal extent intermediate their ends to form a rigid fiber bundle, and such fibers are each provided internally with a cathode lead or cathodic current collector in the form of a wirelike member.